The skin is the largest and most accessible organ of the human body. The permeability of the skin, and its ability to deliver drugs to the blood stream, makes it an ideal drug delivery route. Transdermal Drug Delivery (TDD) systems capitalize on this potential by delivering drugs through the skin, making them easier to administer. Such delivery systems, also known as “patches” have in recent years become an increasingly important means of administering drugs. These systems offer advantages, such as avoidance of the gastro-intestinal tract and “first-pass” through the liver, application close to the site of action, sustained and easily adjustable action, which are typically not achievable by other modes of administration.
In practice, a TDD containing the agent or agents to be administered is placed onto a tissue of a host. The agent, which is releasably stored in a repository of the device, then diffuses or is otherwise transported to the host. Such delivery can be used for topical, transdermal, transmucosal, or other transtissue delivery of the agent to therapeutically treat local or systemic medical conditions. Patch devices can be used for pharmacological treatments, cosmetic treatments, nutriceutical treatments, and/or the like. Such systems have found increasing use in dispensing, in a time-controlled manner, a variety of pharmaceutical ingredients for such purposes as hormone replacement therapy, pain management, angina pectoris, smoking cessation, birth control, and neurological disorders such as Parkinson's disease.
Typical transdermal systems comprise some kind of backing material that contains the drug, reservoir or layer containing the drug, and an adhesive to attach the TDD to the user. The backing material, commonly a polyester, is inert to the drug (or drug formulation) and adhesive and does not permit any of the drug formulation to migrate through it. However, many TDD's include a layer between the backing layer and the drug consisting of an ethylene-vinyl acetate (EVA) copolymer, which is sometimes used to provide adhesion between adjacent layers. However, one disadvantage to using such layers is that delivery of the drug to the user may be slower than would be the case if the EVA layer were not there, potentially resulting in the need for a larger patch size to deliver the desired dosage. Thus there is a need for alternative ways of providing the adhesive function of the EVA layer while minimizing unwanted drug interactions and slowing of drug release.